Add WOFF2 versions of the fonts

Contrary to other web font formats, the new WOFF 2.0 Web Font compression format is optimized for file size, memory usage, and decompression speed.

WOFF2 has been supported in Chrome and Opera for a while now. See https://dev.opera.com/blog/opera-23/ for more info.

static/fonts.less

@@ -2,12 +2,17 @@
 @use-eot: true;
 @use-ttf: true;
 @use-woff: true;
+@use-woff2: true;
 
 .use-eot(@family, @family-suffix) when (@use-eot = true) {
     src: url('@{font-folder}/KaTeX_@{family}-@{family-suffix}.eot');
     src+: url('@{font-folder}/KaTeX_@{family}-@{family-suffix}.eot#iefix') format('embedded-opentype')
 }
 
+.use-woff2(@family, @family-suffix) when (@use-woff2 = true) {
+    src+: url('@{font-folder}/KaTeX_@{family}-@{family-suffix}.woff2') format('woff2')
+}
+
 .use-woff(@family, @family-suffix) when (@use-woff = true) {
     src+: url('@{font-folder}/KaTeX_@{family}-@{family-suffix}.woff') format('woff')
 }
@@ -34,6 +39,7 @@
     @font-face {
         font-family: 'KaTeX_@{family}';
         .use-eot(@family, @suffix);
+        .use-woff2(@family, @suffix);
         .use-woff(@family, @suffix);
         .use-ttf(@family, @suffix);
         font-weight: @weight;